Generally, an engine includes a combustion chamber providing driving torque by combustion of fuel, an intake valve disposed in the combustion chamber and supplying a mixed gas including a fuel, and an exhaust valve discharging burned gas.
The intake valve and the exhaust valve open and close the combustion chamber by a valve opening device connected to a crankshaft.
Recently, research has been undertaken on a variable valve lift (VVL) system that enables different valve lifts depending on a rotational speed of the engine in order to achieve optimal valve operation depending on engine speed.
In the engine having the VVL system, exhaust gas discharged from the combustion chamber may be flowed into the combustion chamber by opening the exhaust valve during a suction stroke.
According to the conventional art, when a vehicle accelerates, since the engine speed and a load increases, boost pressure increases by decreasing opening of a vane provided in a turbocharger. However, as opening of the vane decreases, a front end pressure of a turbine provided in the turbocharger and exhaust gas recirculation (EGR) increases.
Accordingly, an air amount flowing into the combustion chamber cannot follow a target air amount, an air/fuel ratio is deteriorated, and a fuel amount injected into the combustion chamber is limited. Therefore, since the fuel amount injected into the combustion chamber increases in order to output a target torque, fuel consumption is deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.